How can I make my computer better for photo editing?

This is a common question. Below is the response to this question from a Photoshop forum post a M-Tech Technical adviser posted to try and be of some help.
There is a lot you can do to help your photo edits. I can’t promise that you do not have some other issue, but I know for a fact your computer is falling short of ideals. I assume you don't want to know too much about how a computer uses memory, I would be happy to explain in detail when appropriate. To make a long explanation short, you cannot get too much memory. Think of RAM like money, you may have enough to pay the bills but more is always better.4GB is not nearly enough, regardless of your O.S., 32B or 64B. Either way, your program still needs a lot of RAM. the only difference between 32 and 64 bit is how the RAM you need is addressed. I will assume that if you have 4GB you are using a 32 bit OS. This means that almost immediately your computer is running short of RAM and your computer will be using the system drive to make up for the shortage. This means that all the work you do is being swapped back and forth from that drive, your processing is no faster than your drive and bus. While CPU can do multi processing (depending on your CPU) but your drive can only do one file at a time. This means that your OS, all background resources your Photo editing program and let’s not forget the photos and the edits themselves all have to be shuffled back and forth from the small 4GB of RAM to your slow drive over and over back and forth, one file at a time. The more RAM the more stays in memory and the less has to be paged back to the drive, major reason why there can be no such thing as too much RAM for a 64 bit system.
So what can you do, two things. Get a 64 both Operating system so you can max your computers RAM out, This will save you hours of processing by not having to have the O.S. paging to a virtual memory and your program won’t have to page to the drive nearly as much. More RAM means less virtual memory. Not just the photos, every program is a compilation of mini programs compiled to run as a single program, These are call .dll files. Windows , notepad, Photoshop etc.. all use the same .dll files to do the same function common to all windows programs. So if you have enough RAM, once that .dll is fetched it can stay in memory. Don't have enough memory and the .dll will be sent back to virtual RAM on your drive until it is needed again, possibly only seconds later. More and more of your computers time is wasted as these files are fetched and put back. So the more RAM the more of these files just stay in memory to be accessed instantly every time they are needed. So, while you can have enough RAM to run (because of the virtual RAM on your super slow drive) you can see that even if you are not using memory hogging data files, which you are.
That was the first thing, More RAM
The second thing is to get a secondary drive. recall I mentioned that drives can only do one thing at a time. This means that the entire purpose of editing a photo has to wait on the back burner until your system and another background programs have had their time with your drive and system bus. So, if you have a drive just for data, it means that your photos can be getting on with things rather than waiting for their line in the queue. So your photo editing can go as much as twice as fast when it has its own data bus to zip back and forth on. Note, unless you get SSD's, Zipping back and forth is a generous metaphor. HDD's seek rate is around 100 times slower than SSD's.
Now we have covered the two things you can do. Let’s talk briefly about your drives.
There are two schools of thought when it comes to what type of drive to buy.
First is that if your C: is a SSD your computer will boot faster and your programs will start and run faster since each little .DLL making up the program is found and retrieved 100 times faster. BUT, once you have all these .dlls in the huge amount of RAM we now both hope you have, your SSD is going to stop being so much help because if you have more than enough RAM the file sis staying up in RA< and won’t need to be fetched anytime soon. This means that if you don't have enough RAM, the SSD will continue to be a big help because you’re going to go back and forth all day long. How about that second drive? Well since you have that 2nd drive you likely will also use it for storage. Fetching the initial photo won’t be helped much buy a SSD because it is one file. A big file for sure but since bandwidth on a SSD is the same on a good HDD your benefit for single fetches is not that great. Now, if this was a database or audio it would be the opposite. So does this means you2nd drive should be a HDD since a SSD won’t help in fetching a single photo. Yes...and NO. Your primary reason for getting this drive was to use it as a temp/scratch drive. A pace for the work to take place on as it exceeds your RAMs size. Images take so much RAM you can’t hope to have 100% if what you need by way of RAM. So you give yourself a dedicated drive to use as a workbench. Because this will be files and edits zipping back and forth constantly, this drive will benefit from being fast. Do a SSD will most defiantly help you. In short, if the drive will be substitute for RAM, then make it a fast drive. If it is for storage, then go slow if the files are single and large.
You may see now were the need for a third drive can be used. All our professional photographers use three drives, One for the Programs, one for the scratch drive and one for the storage of the images,. This allows for you to get a cheap HDD for storage and a small SSD for the scratch drive and since your C drive won’t be holding everything, your primary drive can also be a smaller SSD as well.